REPORT ON THE RADIOLARIA. 1591 



triangular meshes. The AiilosphEerida dittcr iu the development of the peculiar nodal 

 cavities and astral septa, by which the thin-walled cylindrical tubes *of the articulated 

 network are separated in the stellate nodal points. The Cannosphaerida, closely allied 

 to these latter, also differ iu the articulated network, and further in the possession of an 

 internal concentric shell. The Castanellida are sometimes similar to the Orosphserida, 

 but distinguished by a peculiar large shell-mouth and a network of different shape. 



The Orosphaerida belong to the biggest Rndiolaria, and the lattice-work of their 

 spherical shell is of a ruder and coarser shape than, iu any of the other families of this 

 class. Nevertheless they have been hitherto perfectly unknown, and were first discovered 

 by the Challenger. We have been able to distinguish in the collection four genera and 

 twenty-seven species. This strange fact ma)^ be explained by the circumstance, that they 

 are in general rare, and restricted to a few localities, and that probably all the species 

 are inhabitants of great depths. Complete shells also are rarely found, whilst broken 

 fragments of their big shells, easily recognisable by the coarse irregular meshes and 

 the thick stratified bars, are met with frequently in the Radiolarian ooze of some Pacific 

 Stations, especially at Stations 265 and 268, at a depth of 2900 fathoms. 



The lattice-shell of the Orosphserida is usually spherical, or an endospherical poly- 

 hedron (PL 106, fig. 4) ; rarely one axis is somewhat prolonged, so that the shell 

 becomes slightly ellipsoidal (PL 106, fig. 1). Its diameter is usually between 2 and 3, 

 often also between 2 and 1 mm., rarely more than 3, or less than 1 mm. The 

 largest shells observed attained 5 to 6, the smallest 0"5 to 0"6 mm. Their general 

 habit is veiy characteristic, so that they may be easily distinguished from all other 

 spherical lattice-shells, especially from the Castanellida and from the simple Monosphaerida 

 (Cenosphera, Acanthos2)hcera), with which I confounded them in the beginning (hence 

 the first shell observed, figured in 1878, was placed among the Monosph^rida in 

 PL 12). A closer examination of the coarse network and of the peculiar structure of its 

 thick bars always enables one to recognise even small isolated fragments of broken shells. 



The meshes of the coarse network exhibit in all observed Orosphserida a very irregular 

 form and unequal size ; the majority are usually more or less quadrangular, more rarely 

 they are triangular, pentagonal or hexagonal, very rarely rounded. They are often 

 arranged in parallel rows, which seem to be determined by prominent crests, connecting 

 the bases of the radial spines (PL 12, fig. 1; PL 106, fig. 4, &c.). The diameter of the 

 meshes is usually between 0'05 and O'l, often O'l to 0*2, rarely more than 0'25, or less 

 than 0'025 mm. In Oroplegma, which develops an outer loose, spongy shell around 

 the inner primary shell, the big meshes of the former become much larger and very 

 irregular (PL 107, fig. 1). 



The coarse bars which separate the large meshes of the u-regular network are very 

 thick and massive, cylindi'ical, usually of unequal thickness, straight or slightly curved, 

 never angular or prismatic. Their diameter is usually between O'Ol and 0"02, rarely 



